The present invention relates to a fundus camera (retinal camera), and in particular to a fundus camera, by which it is possible to achieve infrared fluoresein angiography.
Fundoscopy is one of the important medical examinations to check health condition, and it is to examine vascular conditions of the retina. A fundus camera is used for photographing the conditions of the retina. In recent years, there has been proposed a fundus camera, by which it is possible to perform infrared fluoresein angiography by injecting fluorescent dye into blood of the patient to be examined and by taking fluorescent vascular image using infrared light.
Description is now given on a conventional type fundus camera for infrared fluoresein angiography.
Into blood of the patient to be examined, indocyanine green (in the following, it is shown as ICG), a fluorescent dye having absorption peak at 780 nm in infrared range, is injected. As a light source for illuminating measuring light into the retina of the patient, a xenon lamp is generally used, and only infrared light is projected. Specifically, an exciter filter is provided on projection side, and it is to transmit the light of the wavelength range to be absorbed in ICG and to cut light with longer wavelength. Infrared light is irradiated through this exciter filter. As shown in FIG. 2 by the curve 27a, ICG in blood absorbs infrared light having a peak at 780 nm, and fluorescent light having central wavelength of 810 nm as shown by the curve 28a in FIG. 2 is irradiated. A barrier filter is installed on light receiving side, and this transmits the light in fluorescent light wavelength range and shuts off light with shorter wavelength. As a result, only fluorescent light is received, and an image of retina blood vessels can be photographed at high resolution.
On the other hand, if albumin in blood is bonded to ICG at a certain period of time (about 30 seconds) after injection of ICG, the peak of absorption wavelength is changed from 780 nm to 805 nm as shown by the curve 27b in FIG. 2. At the same time, the peak of fluorescent light wavelength is also changed to 835 nm as shown by the curve 28b in FIG. 2.
Therefore, it is not possible to photograph with high resolution when a certain period of time has elapsed.
Taking such change of fluorescent light wavelength into account, a fundus camera has been proposed. In this camera, the exciter filter and the barrier filter are installed to match wavelength range after a certain period of time has elapsed in order to photograph the image of retina.
One of the advantages of infrared fluorescent angiography is the possibility to identify behavior of blood with a fluorescent dye injected into it. In the infrared fluoresein angiography, continuous photographing of moving images with the lapse of time or continuous photographing of numerous static images are performed with the lapse of time in order to record the change of the condition from injection of the fluorescent dye.
In the former case among the conventional cases, proper angiography can be achieved in initial stage when binding of albumin in blood with ICG is not started yet. But, when the peak of absorption wavelength and fluorescent light wavelength is deviated to longer wavelength after the binding of albumin with ICG, irradiation light beam is shut off by the exciter filter, and illumination light, i.e. fluorescent light, is shut off by the barrier filter, and this makes it impossible to perform effective angiography after a certain period of time.
Among the conventional cases, proper angiography can be achieved after a certain period of time in the latter case, while effective angiography cannot be performed in the initial condition, inconveniently.